Curable epoxy resins are well-known in the industry today, their commercial exploitation having its beginnings in the late thirties and early forties with the discovery of various methods and agents for converting the usually viscous liquid or brittle solid intermediate epoxide into a useful end product. In the United States one of the earliest disclosures covering the curing of epoxides was U.S. Pat. No. 2,324,483 (1943) wherein is described the curing of phenolic epoxide resins with dibasic acids. Since that time a wide variety of curing agents have been discovered which will affect the conversion of the liquid or solid epoxide into a useful end product.
These curing agents generally fall into one of two categories known as catalysts and reactive hardeners. In the former the agent functions to initiate the polymerization creating direct linkages between the many intermediate molecular weight epoxy molecules. Curing agents falling within the catalyst classification include bases such as tertiary amines and acidic materials such as boron trifluoride and amine complexes thereof. In the latter classification, i.e., reactive hardeners, are included various amine compounds such as aliphatic amines as represented by ethylenediamine (EDA), diethylenetriamine (DETA) and higher members of this series; hydroxy aliphatic amines such as N-(hydroxyethyl)diethylenetriamine; acrylonitrile adducts of primary-secondary aliphatic amines; primary-tertiary aliphatic amines such as diethylaminopropylamine; cyclic secondary amines such as piperidine; aromatic primary amines such as m-phenylenediamine; phenolic tertiary amines such as (dimethylaminomethyl)phenol and salts thereof such as the 2-ethylhexoic acid salt and acid anhydrides representative of which include phthalic anhydride, pyromellitic dianhydride, dodecylsuccinic anhydride and hexahydrophthalic anhydride to name but a few. The most frequently employed curing agents are those that function as reactive hardeners and, of these, the amine based curing agents are the most widely used.
Although literally hundreds of curing agents have been tried or claimed, there still remains a need for curing agents which will effect the curing of epoxy resins to provide useful end products exhibiting good thermal properties and good moisture and chemical resistance characteristics, and there is particularly a need for curing agents which, when blended with epoxy resins, will provide mixtures exhibiting extended useful potlife. Thus, it is an object of this invention to provide novel curable compositions comprised of an epoxy resin and a novel epoxy curing agent. It is a further object of this invention to provide novel curing agents for epoxy resins which, when mixed with said resins, provide curable compositions exhibiting extended useful potlife. It is a further object of this invention to provide a method of curing epoxy resins employing the novel curing agents herein described. These and other objects will become apparent to those skilled in the art upon the reading of the following descriptions and disclosures.